In my U.S. Pat. No. 3,677,618 issued Jul. 18, 1972 entitled Binoculars Having Stabilizing Reflectors, I disclosed an optical instrument having a single objective input, paired binocular outputs at attached eye pieces, and a folded light path therebetween. With respect to the objective lens, a stabilizer cell having a mirror was positioned to cause one of the folds in the light path at approximately one half the focal length of the objective.
The stabilizer cell utilized is described in Humphrey U.S. Pat. No. 3,711,178 Issued Jan. 16, 1973, entitled Mirror Stabilizer Having Space Reference Motion. The construction and function of this device can be briefly set forth.
A stabilizer cell of cylindrical configuration confining a transparent fluid bath was utilized. A circular mirror was placed within the cell and suspended on a rubber band extending longitudinally of the chamber and at least partially buoyantly supported by the transparent fluid. The mirror faced a circular transparent wall of the stabilizer cylinder and reflected light incident to the mirror through the transparent wall from the mirror out through the transparent wall.
Operation of the stabilizer is easy to understand. When the stabilizer cell under goes motion, the confined fluid within the stabilizer cell likewise under goes motion. The mirror under force of the fluid motion of the transparent fluid in the stabilizer moves with respect to the stabilizer in inertial stabilized motion with respect to space. At the same time, the rubber band biasing the mirror provided a restoring force. The mirror tended to return to a neutral position with respect to the optical instrument being stabilized. There resulted a relatively satisfactory scheme for optical stabilization.
This type of stabilizer does have its drawbacks. Specifically, the transparent wall of the chamber in combination with the transparent fluid and the optical interfaces associated with the window degraded the optical quality of the stabilizer. This degraded optical quality was magnified by the power of the instrument. Further, and since the mirror was suspended in a fluid tight environment, user adjustment of the mirror suspension in the field was not practicable.